That's a real nice pen but, yes, it appears you are not sanding to a higher enough grit before you start final polishing. A rough rule of thumb is that the grit for subsequent passes should be no more than double the number of the current grit. So, for example, if I'm currently at 150, the next grit should be 300 or less (I choose 220). Then from 220 go to 400, 800, 1500, etc. I like to wet sand but in any case I think it's important to not contaminate subsequent steps with previous step swarf (wipe it down thoroughly after each step). Final polishing options are all over the place - Novus, McGuires, the Beall buffing system, etc.
Develop your own procedures. It's worth the effort.